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April 1986, the body of a 15-year-old girl has been found in woods near a railway line in Surrey. She has been raped and strangled. The murder has startling similarities to another, of a young woman four months earlier near a railway line in northeast London.

At its initial stages I don't think anyone envisioned just how big it was going to be. It was only as the investigation progressed over the last two, two and one half years that the magnitude of it all unfolded.

The police were on the killer's trail, but it would take a new investigative technique to help unlock the case. Criminal profiling, a technique that would later prove controversial in the famous unsolved murder of Rachel Nickell.

In February 2001, the last piece of a jigsaw, that had tormented police for nearly 20 years, finally fell into place. David Mulcahy was found guilty at the Old Bailey of 15 counts, three of murder, the rest of rape and conspiracy to rape. He was convicted largely because of the evidence of one man, his former friend and accomplice in the rapes and murders, John Duffy. That's how the story ended.

But it began 20 years before, in 1982, with the rape of a young woman near Hampstead Heath. The victim described being attacked and raped by two men with knives. Over the next four years there were to be more such rapes.

Here is one of the gaps that was used to take the victims up onto the heath. Once onto the heath, they were then taken-- and one in particular-- something like one quarter of one mile over into the heath, through the woodland into a park, where only the attackers would have known that park was. It wasn't spontaneous onto any piece of [INAUDIBLE] ground. They had reconnoitered the area well and truly. They knew the area, and it was planned, in short, like a military operation.

All the rapes had a pattern. And to catch the rapists the police would turn to what, in Britain, was a relatively new investigative technique, criminal profiling. It was the FBI that really put criminal profiling on the map. In the 1970s, at their new Academy in Quantico, Virginia, the FBI began to use psychology to help solve crime and catch criminals. One of its pioneers was Robert Ressler.

Criminal profiling is creating a behavioral composite of a person who has committed a crime, where that person is not known. It give the age, a race, a sex, and various demographics about that individual that would portray him psychologically in such a way that it would aid the investigators in identifying a logical suspect.

Criminal profiling is the application of psychological or behavioral expertise to understand, investigate, and interrupt violent or violence-prone individuals. In the United States we use a couple of different terms for it. We call it criminal profiling, we also call it criminal investigative analysis, or crime-specific consultation. Profiling is the most common term that we use, though.

Profiling begins with information gathering. Information from the crime scene is pulled together and used to build up a profile of the offender.

The FBI process of profiling falls into a sequence, essentially. First of all, to do a profile upon a request, usually by local police officers, you have to have behavioral inputs. You have to have the crime scene information, you have to have the reports, the crime scene photographs, the police reports, the psychological reports if, in fact, there's anything along that line, which normally you wouldn't have much in that area because you're dealing, keep in mind, with unknown subject. But if there's any psychology involved, you need to know about that.

You need, as I said, the crime scene photographs, color photographs, a video of the crime scene, if possible, and all angles. And also, information along the lines of anything that has come up in the investigation, to include forensic information from the forensic laboratory and ballistics, or anything along that line, hairs and fibers, anything, DNA that might have been collected. You need the pathologist reports and medical reports, the autopsy reports and photographs from the autopsy.

The more information a profiler has to go on the more useful the profile will be. Repeated patterns of violence can begin to give away the identity of the perpetrator. That's why criminal profiling seems to work best when used to track down serial rapists or killers.

Profiling is only suitable for certain types of crimes, in particular, ones in which there is a long interaction, in most cases, between the victim and the offender. So traditionally, homicides, rapes, especially serial rapes, are the ones in which profiling is used. Those are the areas where it is most likely that you'll be able to detect something about the offender from the way in which he carries out the crime.

It's often used in unsolved crimes, which are of an extremely violent nature, in which we're trying to take a look at a situation where maybe the case has come upon a dead end and we're reviewing it, extensively, to determine if there's something we've overlooked in terms of what the perpetrator's revealing about himself through what he did at the crime scene, what he said. Other times criminal profiling is used when we know who the bad guy is but we're trying to understand better why he did what he did. And sometimes that profiling information is used to share with the court, or with investigators that are trying to approach this individual to investigate other aspects of the crime.

Putting together all that information, it carries you onto a decision making process as to just what type of crime you're dealing with. Is it organized, is it disorganized, is it mixed? Are you looking at a crime of a mentally ill person, or very much about a calculating serial killer?

It starts now giving you the basic information that you need to formulate the actual criminal profile. What's his lifestyle? Where does he fit in the socioeconomic status of society? Where would he reside, or work, or operate in relationship to the crime scene? Is he a transient, is he passing through, is he local, is he living in the area?

And the profile then, of course, is provided to law enforcement. What the profiler cannot do, and it is not supposed to do, is get involved in the actual investigative steps, or get too deeply into the investigation. They're consultants.

By the end of 1985, in North London, the police still had a series of unsolved rapes on their hands. But a pattern was emerging. All the women were raped, often near Hampstead Heath, late at night, on the weekends, close to railway lines. Then, the pattern of violence turned deadly.

19-year-old Alison Day was raped and murdered near Hackney Wick station in northeast London. When police found her body in the nearby canal she had been strangled with a piece of cloth used as a ligature around her neck. Her wrists were bound.

Striking feature of this murder was, firstly, that she had got a ligature tied around her neck, the ligature being held in place by a piece of wood, which had been used to tighten it, and had been lodged behind her ear, thus preventing it from coming loose. Secondly, her hands were tied. Both, unusual features in themselves.

More horror was to follow. Police turned to criminal profiling.

The story starts, as far as I'm concerned, in the spring of 1986 when a 15-year-old Dutch national was reported missing from home.

Maartje Tamboezer was a 15-year-old Dutch girl. She'd gone misting when cycling to her local sweet shop in Horsley, Surrey.

She was found in woodland not very far away from her house. The senior investigator then came to the house and informed the parents that their daughter has been found, but she was, unfortunately, dead.

An unusual feature of this murder was also the fact that the ligature was around the neck, again, a piece of wood had been used to tighten the ligature. And again, the piece of wood was wedged behind the ear, thus preventing it from slipping. Tying had also been used.

Whereas in the first murder, of Alison Day, she had been immersed in the canal, thus eliminating forensic evidence. In the second murder, with Maartje Tamboezer, an attempt had been made to burn the body. Wood had been piled underneath the body, tissues had been ignited, most of it in and around the pubic region, thus trying to, again, eliminate any forensic evidence.

These two murders were linked by the senior investigating officers because of their unusual methods. At that stage, it was unique, to say the least, of this form of ligature being used.

The police were now investigating two murders. Both women were raped and strangled. Could those be linked to the Hart inquiry, the investigation into the earlier North London rapes?

Lots of similarities were discovered in the murders. The Hart inquiry had also been consulted, and it was also discovered that there were similarities between the murders and the rapes.

The prime similarity being the fact that the victims had had their hands tied behind their backs. In some cases, the tying was unique in so much as instead of the hands being tied the victims' thumbs had been tied or the fingers had be tied individually. Also used in the tying up, in some instances, was a material called [INAUDIBLE], which is, in fact, a paper string normally used in the laundry industry. And this also proved a link.

Police in the profiling team now something very concrete to go on, but also something very sinister.

When the murder of Maartje Tamboezer was linked to the murder of Alison Day it was linked because of a peculiar method of killing. That, really, was an outstanding link. There was a view that said, well, we've got what appears to be a sexual murderer in two places, at Hackney in East London and Horsley in Surrey. And the possibility is that we've got a sexual criminal operating in North London that could've been responsible for both of them.

So there was no definitive link there, really. So the way in which we went about that was to look at the sexual offenses rather than the murders because there'd been, actually, the attack on a live victim, and your case material is a lot richer. For example, you've got descriptions of people, and descriptions of an event. And so the decision was to work on that material to see if there was any consistency in it at all that would indicate a serial offender.

There are different approaches to profiling. Some experts use their knowledge of certain types of criminals to create a profile. Others examine patterns of crime to identify which geographical area the perpetrator is most likely to live or operate in.

The clinical people will base their contribution to the investigation on the experience of having dealt with the kinds of people who will have committed the crimes that we are investigating, so people who have invested a lot of their life in dealing with sex offenders. They will have a lot of information to offer about the lifestyle of sex offenders that could be helpful to the investigators in trying to identify people who would fit the profile. On the other hand, there are other investigators who spend their time looking at the pattern of offenses, and as a result of that, identifying the areas, geographically, that the investigators should concentrate on, trying to identify people with previous history who would live in that particular locality.

One should think about a crime, particularly a violent crime, as the canvas on which the perpetrator projects himself. What he does at the crime scene serves the purpose of whatever he's trying to accomplish, and the unique way that he does it says something about who he or she is or may be. And what we're trying to do in the process of profiling is separate those aspects of the crime that are just necessary to do the crime, the so-called modus operandi, versus those things which are called the signature, those parts that were not necessary to perpetrate the crime but that the offender does because that's part of the reason for why he does it. And that's what we call the signature.

So part of what we're looking for in these situations is a distinction between the modus operandi from the signature, those very personal aspects that were not necessary to accomplish the crime or to get away with it. That can be like in some cereal homicide cases, if the person has a particular way that they torture the person, they use a particular knot, or they use a particular weapon, or it's hands-on as opposed to using a handgun.

Is it necessary for the person to kill somebody to have it be hands-on? No. That suggests that the person likes that kind of personal approach to killing their victim versus another situation where the person always uses a gun, and that's just simply because it's easy.

Because profiling studies criminal behavior, some of it illogical, it's closer to an art than an exact science.

And I've come to the conclusion over nine years, now, of working in and around this field that, to a large degree, it might be more appropriate to be labeled philosophical profiling rather than psychological profiling because, ultimately, it's about thinking. It's about thinking in ways in which police officers are not trained to think. And that's not necessarily the purpose of the training regimes because it takes many years to develop the background of expertise in criminology and in forensic and abnormal psychology. And it's not really practical to train all police officers, or even, necessarily, a minority of police officers in those kinds of things.

It's necessary for us to go outside for all kinds of expertise, amongst the hard sciences, when we're investigating a serious crime. And I don't see there's anything to be ashamed of in going outside to the soft sciences in exactly the same way. And murder is the crucial one where you've got to reconstruct the sequence of events in order to understand the interaction between the murderer and the person who's been murdered. And that's where the art of profiling is separated from the science because there's a leap of logic involved.

You see certain effects and you use logic, as well as psychological understanding, in order to work out what must have happened, and how, and why. And from that, you're actually inferring the preferences of the offender, the preferences as in the way they function, the way they think, their attitudes towards the victim. And you can extrapolate that to work out some things about their thinking patterns and about the kind of person they are. That's essentially the key to it.

The profiling team working with Surrey police and pulling all the information from the North London rapes and the two murders began, painstakingly, to build up a profile of the railway killers. It began to produce results.

If I remember right, it was probably one piece of paper, it may have been two, but it contained a number of points that would later be compared with a prime suspect, when it came, and were found to be accurate. But the points would have indicated an age range, an ethnicity, perhaps, a height. Perhaps an idea of the offender's ability to react and interact with people. So it would give a view of his marriage, or whether he'd got children, and so on.

That's, if I remember right, how it was listed. And there are lots of things aren't always that much help to you. But the question of where a person may live, what age range they fit, what kind of criminal history they may have, are all directly applicable to the investigation because they can be used to prioritize whatever suspects come in.

The police knew they were looking for two men, and they had a strong profile for one of them. A white man, short in stature, who lived or worked in North London. He probably knew the railways, might be a loner, who, perhaps, had difficulty forming relationships with women.

Usually, the profile will come in at a stage where you've generated a number of possible, or even likely, suspects. And the profile can then be used to screen those, and to make some kind of judgment as to which is the most likely person to have comitted the crime. And in that way, it can be an almost risk-free way of applying the profile because, If you've got 12 suspects and no real reason to interview one before another or to try and eliminate from the investigation one before another, then applying the profile as a screen and setting them in order, the profile can help you to solve the case more quickly. But if not, then you've not lost anything because had to see the 12 of them anyway.

Police were drawing up a list of suspects for the North London rapes and the Hackney and Surrey murders. Would any of them turn out to be the killers? It wasn't long before the net starts to close in on one of them.

In May 1986, police were investigating a series of rapes and the murder of two young women. But worse was to come. A month after the killing of Maartje Tamboezer in a wood in Surrey, the killer struck again. 29-year-old Anne Locke was raped and murdered near the railway station at Brookmans Park in Hertfordshire.

Her body wasn't found for some considerable time. And when it was found on a railway embankment it was badly decomposed. No ligature was found around the neck, but it is, because of the decomposition, it was impossible to say whether, in fact, a ligature had been used. But there's certainly a scarf that she had been wearing had been placed around her lower face, and a sock had been forced very deep into her mouth, into the throat, which in itself would have caused asphyxiation.

Binding had also been used on her. In this case, her fingers had been individually tied together, and then tied behind her back. All three murders were linked because of their unusual patterns.

Modern criminal profiling was driven by the huge amount of research done by the FBI during the '70s. It became known as the Criminal Personality Research Project, and was based largely on interviews with serial killers. The research was headed by former FBI profiler Robert Ressler.

After identifying and amassing a number of outside professionals, people, psychiatrists, psychologists, various people outside the FBI to assist me in this project, I then trained a number of FBI agents to assist me also to gather this information. I held a special symposium from all around United States, brought in about 55 various FBI agents, and gave them two weeks of training to train them to assist in this research project to gather data and to identify subjects for interview.

Once that was done, I began, with my teams, going around the various prisons around the United States, going into the penitentiaries and interviewing selected violent offenders. And over a period of a number of years, probably seven or eight years, I probably did 55, 65 different interviews, of which we decided which ones we were particularly interested in that would constitute a good database for studying violent criminal offenders, most of which were sexual offenders.

The thrust of the project was sexual-oriented homicides. And what we found is that the subjects that we had identified had killed multiply. So it became known as the Serial Murderers Project.

After gathering information about the killers, such as their background, family history, and criminal records, Robert Ressler was ready to meet them.

I would spend at least a half a day, sometimes a full day, in the prison looking at the prison records, the prison files, before I would actually go into the interview. So by the time I got to the interview with the individual I knew more about him and his crimes than he did, for the most part. What he would still have in his own mind would be motivation, some of the fantasy that would drive him to his crimes, and these were the things we were looking for the most-- in that direction-- because the fantasy, the motivation, these are things that are not in the record.

And what I found over a period of time is that very early, bizarre fantasies, going back to preadolecense, were the roadmaps that carried these individuals to their violent crimes later in life. So that's what I was searching out, is the filling in some of the blanks on interpersonal relationships within the family, relationships between mom, dad, peers, significant people in their lives, and, of course, the development of the motivation that would lead them to their crimes. And, of course, the fantasies were very, very important.

Robert Ressler had the pleasure of meeting all kinds of people during his research.

The more outstanding ones was interview with a vampire. It was an individual by the name of Richard Chase, who had killed seven people, I think, over a period of about a week. And he was killing them for their blood.

This guy was cutting open the victims and taking their blood and internal organs in vessels, that he would take from the kitchen, and carry away these body fluids and body parts to his apartment, where he would actually involve himself in vampirism and cannibalism. He had a delusion that he had some condition where his blood had been drying up and turning to powder, and he had to replenish it through ingesting human blood.

One individual was 6' 9", weighed almost 300 pounds, and had an IQ of 150, a very large man. And he had killed 11 people including his grandparents and his mother, and the rest were young women, college girls for the most part. He would decapitated his victims, snap their necks and eventually decapitate them.

Due to a little confusion within the prison system I became trapped with him in a small interview room for about 45 minutes above and beyond the time that I had planned on being with them him. And there was no guard responding to my assistance when I wanted to get out of there. And I had to, more or less, I guess you'd call it, negotiate with this individual who had started talking in terms of killing me, breaking my neck, and snapping my neck and twisting my head off.

When he realized his guard was not coming because the guard was diverted by serving dinner to inmates and would not be around for another half-hour or 40 minutes, he started psychologically torturing me by telling me how easy it would be to break my neck and actually to twist my head off. So as I said, I fell into a negotiation role with him, trying to negotiate for my own skin. So that was memorable.

Robert Ressler's research was published, and provided all sorts of investigators with a clear insight into the workings of the criminal mind. Police in the case of the railway murders now had a profile of one of the killers. But it took an extraordinary turn of events to identify a man who fitted the profile. A woman came forward to say that she had been raped by her ex-husband, one John Duffy.

The circumstances of the attack on his ex-wife are that he met her by appointment. He had arranged to meet her in a park, again, in North London. They met, and during the course of that meeting John Duffy raped his ex-wife at knife point. Now, what heightened interest was the fact that he was in the right area, he was of the right age group, that he has a propensity to do rape. After all, he raped his ex-wife.

It was during the course of her making the statements regarding the alleged rape on her that she related instances of how he had experimented with her sexually, and that bondage played a large part in his sexual fantasies. She also said that on one occasion he had presented her with a Walkman stereo, and told her that it had come from a girl that he had raped. Obviously, as a result of this, he then became a prime suspect.

Duffy was 28 years old, about 5' 6", recently separated from his wife, and had lived all his life in North London. He had also worked for British Rail. He fitted the profile.

The profile showed him as being a loner, which was correct. It showed him as living in the center of the rape area, which was Hampstead. And in fact, he did live in Hampstead. It showed him as being an introvert, where, in fact, he was the introvert while Mulcahy was the extrovert. He had an extremely good knowledge of the area.

The profile, whilst it was true, possibly, to start with, that he worked alone and didn't come into contact with females-- was true whilst he was working for British Rail. But then when he worked for the local council his job as a carpenter took him into homes where there were females. And, as I say, profiles can change, obviously, with the result of what occupation.

It was also true in respect of his marriage, that he wasn't married. And when he first started he wasn't, had no children. However that did change when he did become married, all be it, he still never had any children.

When the actual descriptive file on John Duffy came back, then that became really quite a high spot, because caution prevails, really, when you're involved in this. You're saying to people, now look, come on, it might not be him, but he's certainly worth a very strong look. And his history was minor. He lived in the right area that the profile put it [INAUDIBLE]. He'd actually had an allegation made by his ex-wife that she had been raped by him after they'd parted, after they separated. So it was a lot of detail there that made him really stand out, particularly where he lived.

Former FBI profiler Robert Ressler has devoted 40 years of his life to studying the worst sorts of crime and violence. He's left is mark on crime writing, real and fictional.

Back in 1981, I was contacted by Tom Harris, who wrote the book Red Dragon, which in fact, first introduced Hannibal Lecter to the world. And I had a distinct part in, I guess the, birth of Mr. Lecter, Dr. Lecter, I should say to keep things proper. At the same time, the Red Dragon book became a movie called The Manhunter. And in 1985 I was re-interviewed by Tom Harris for a book that he was writing, which was called Slience of the Lambs, which became the film that is so well known today.

The personality of Hannibal Lecter was a composite of a number of serial killers that have operated in years past. There is no one individual that Hannibal Lecter is patterned after. People, to this day, from time to time, will ask me, is Hannibal Lecter still at large? And they believe him to be a real person. He's fictional.

In 1988, at the Old Bailey, John Duffy was found guilty of the railway rapes and murders, and sentenced to life.

I don't think profiling nailed Duffy. And I don't think profiling actually nails anybody. It's a tool. Once you've got a suspect and you've got a profile, compare them. And if the suspect meets the profile, well then, it prioritizes him being seen by police officers.

It doesn't provide evidence, it never will provide evidence directly of a person's involvement. It will only suggest that this is the best possible, or probable, background of a suspect. And then you could have hundreds of suspects who fit the profile, or you may, indeed, just have one or two. [INAUDIBLE] just see him first. It's a very simple principle.

It's also a non-risk situation. You're not asking the investigators to abandon what their intuition and their experience will tell them because, again, this comes from my experiences with the FBI and [INAUDIBLE]. What they say is if a police officer comes up with a suspect that doesn't fit the profile you're not going to ignore him anyway. And you shouldn't ignore him. Don't rely on the profile to be everything. It's a tool to help people along.

Early in 2001, nearly 20 years after the first victim had been raped, the final chapter of the railway rapes and murders was written. From his prison cell, Duffy named his childhood friend, David Mulcahy, as his accomplice. Mulcahy was found guilty and got a life sentence. Profiling had helped put the railway murderers behind bars.

Duffy and Mulcahy, the perpetrators of their offenses, are now securely locked away, never to be released.

But there is another major case, in which the use of criminal profiling turned out to be much more controversial.

The police were beginning to get very desperate that they wouldn't solve this crime despite a huge amount of media interest in it, and massive public disquiet that somebody could be killed in broad daylight in the particular tragic circumstances she was killed.

Rachel Nickell was murdered on Wimbledon Common on a summer's day in 1992 as she walked with her very young child. The murder excited a huge amount of publicity, firstly, because it took place in broad daylight, and secondly, that she was killed in a place regarded as a beauty spot with her child with her. She was found in a public place, having been stabbed on numerous occasions.

And immediately, appeals went out for a man seen washing clothes in the stream within a very short space of the scene of the crime, and indeed, for another man seen running down the A3. These two people later became known as the long-haired photo FIT and the short-haired photo FIT. The investigation went cold.

Rachel Nickell was 23. She lived with her boyfriend not far from Wimbledon Common, southwest London. She was bright and attractive with no known enemies and no reason why anyone would kill her.

There was no forensic evidence at the scene of the crime that could be attached to anybody. And so, about September of the following year the police were beginning to get very desperate that they wouldn't solve this crime despite a huge amount of media interest in it, and massive public disquiet that somebody could be killed in broad daylight in the particular tragic circumstances she was killed.

The police went to forensic psychologist Paul Britton, who began to build up a profile of the killer. We asked Paul Britton if he wanted to participate in the program, but he said he didn't want to talk about the Rachel Nickell case.

The profile was somewhat vague, but it was a person who would be regarded as a loner with very few friends, or living at home with one of his parents or both of his parents, with solitary hobbies, no girlfriend, unlikely to drive a car, probably rode a bike, perhaps, unusual hobbies, for instance, Satanism or an unhealthy obsession with pornography. It It was the sort of profile that anybody using a bit of common sense would expect of a killer who'd killed somebody in those particular circumstances. He also concluded that the killer would be a stranger to the victim, which was a very important aspect of the profile.

The police were now armed with a profile but no leads. But then a breakthrough. Crimewatch broadcast two video FITS, the man seen washing in the stream, and the man seen running towards a nearby council estate.

The police received many calls. Some said that one of the video FITS looked like Colin Stagg, a 29-year-old single man who lived alone on a housing estate near the Common.

He was taken to the Wimbledon police station. He was interviewed for three days. At the end of those three days there was no evidence, and they released him without charge. He answered every single question over a period of very many hours. The interviews spanned almost 600 pages, but he answered all their questions. There was no evidence, and they released him without charge.

He was, in fact, however, taken to Wimbledon Magistrate's Court because in the course of the interviews he confessed to having occasionally sunbathed nude on Wimbledon Common. As a result, the police charged him with indecent exposure, took him to Wimbledon Magistrate's Court, he pleaded guilty and was fined. And from that comes the myth that he had previously been convicted of sexual offenses.

Unfortunately for Mr. Stagg, an old pen pal recognized his face, and contacted the police because a few years earlier they had been pen pals. And the correspondence had ceased when he had sent her a rather explicit sexual fantasy letter, which had upset her, and she'd stopped the correspondence. But when she saw him on the television she came forward with her letter and gave it to the police.

Armed with the letter, the police asked Paul Britton whether an undercover female officer, given the fictional name of Lizzie James, would be able to strike up a relationship with Stagg to see if he revealed any involvement in the killing.

What was particularly cynical about this was that the police knew full well that Stagg was a very lonely individual, desperate for a relationship with somebody. And so, armed with the introduction, they began to establish a relationship by correspondence, but at all stages, with the promise and the offer of eventually meeting and eventually having a full-blown relationship. The relationship between Stagg and Lizzie James was only by correspondence at this stage, although they did meet later.

And there was never anything physical between the two of them at all. But they did begin to exchange more and more extreme fantasies. The point was that the profiler needed these fantasies to become extreme so that he could conclude either that Stagg was innocent, according to him, or to say that these fantasies are identical to the fantasies I would expect the killer to have.

Lizzie pretended to Stagg that she had fantasies that turned her on, things which most people would find upsetting. Lizzie James introduced things such as humiliation and domination. But more significantly, they designed a fantasy tape that was sent to Stagg, which involved the sacrificial murder of a woman and child in a satanic rite in a forest. She and the leader of this coven, thereafter had sex in the blood of the victim. She wrote to Stagg in those terms, and said I can only be turned on, effectively, by somebody who has gone through the same thing as that. It's a shame you didn't kill Rachel Nickell.

Colin Stagg said he hadn't committed the murder, but the fact that he had knowledge of the position of the body from a photo he'd been shown when arrested, did him no favors.

This caused great excitement in the police camp because they believed that the photographs they had shown Stagg couldn't possibly have revealed what he was describing to Lizzie James. And shortly thereafter, they arrested him.

Gisli Gudjonsson is the psychologist who was asked to assess him.

I was commissioned by the defense to conduct an evaluation of Mr. Stagg in terms of his personality, to try to understand him a bit better, and try to establish whether or not he did have the kind of features that had been predicted by Mr. Britton's profile. And secondly, I analyzed the detailed interactions between Mr. Stagg and the undercover policewoman in the correspondence between them in order to evaluate whether or not the deviant sexual fantasies had emerged during those interactions were due to influence, or whether or not they were due to genuine fantasies.

Colin Stagg was in custody for months before the case came to trial.

I assessed Mr. Stagg psychologically. I was commissioned to study in detail the interaction between Mr. Stagg and the undercover policewoman, who has been asked to try-- presumably asked to elicit a confession from him, or to elicit some sexually deviant fantasies that would help to convict him. I found no evidence at all to indicate that he had some kind of deviant sexual fantasies or preferences or thoughts. He was a sexually inexperienced individual, there's no doubt about that. And that's also public knowledge. And I found nothing particularly in his character to indicate that he was psychopathic.

There were five days of legal argument before the judge concluded that the evidence was inadmissible. And he concluded that the Crown could not rely on any of the Lizzie James and Stagg correspondence. Within seconds thereafter, the prosecution offered no evidence because there was no evidence against Colin Stagg. And Stagg was found not guilty and free to go.

The Rachel Nickell case remains unsolved. Profiling has had its successes. It has helped put vicious criminals behind bars. But there are dangers inherent in any investigation which seeks to make the profile a main piece of evidence.

I think it becomes dangerous also when the police take information from a profile and become two overzealous. And I think the Colin Stagg case in the UK demonstrated how the police investigation became directed, strictly, at one individual, and did not take into account the possibilities of other suspects. They got involved in tunnel vision, you might say, and going overboard with a investigation above and beyond that which should be required from the direction of the profile.

I think psychologists have a very valid role to play in crime detection. The police have, obviously, got a great deal of expertise built up over many years. A psychologist can bring a different perspective to the inquiry, and can, actually, add to the police investigation providing they do their profiling correctly.

My personal view on criminal profiling is that it provides no more than an investigative tool to the police. The minute the police cross the Rubicon and try to rely on it as evidence is redolent with danger, as indeed, was shown in this case, where the profiling hijacked the whole investigation, and led to a man spending 13 months in prison when he didn't deserve to be there.

Criminal profiling has caught the imagination because it tries to classify and even predict the way criminals might behave. It's not a cure-all, and it's not infallible. But it is a valuable tool in helping to solve crime and increase our understanding of the inner workings of the criminal mind.

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